It is known that polysiloxane-polycarbonate block cocondensates have good properties with regard to low-temperature impact strength or low-temperature notched impact strength, chemical resistance and outdoor weathering resistance, and to ageing properties and flame retardancy. In terms of these properties, they are in some cases superior to the conventional polycarbonates (homopolycarbonate based on bisphenol A).
The industrial preparation of these cocondensates proceeds from the monomers, usually via the interfacial process with phosgene. Also known is the preparation of these siloxane cocondensates via the melt transesterification process using diphenyl carbonate. However, these processes have the disadvantage that the industrial plants used therefor are used for preparation of standard polycarbonate and therefore have a high plant size. The preparation of specific block cocondensates in these plants is often economically unviable because of the smaller volume of these products. Moreover, the feedstocks required for preparation of the cocondensates, for example polydimethylsiloxanes, impair the plant, since they can lead to soiling of the plant or of the solvent circuits. In addition, toxic feedstocks such as phosgene are required for the preparation, or these processes entail a high energy demand.
The preparation of polysiloxane-polycarbonate block copolymers via the interfacial process is known from the literature and is described, for example, in U.S. Pat. No. 3,189,662, U.S. Pat. No. 3,419,634, DE-B 3 34 782 and c.
The preparation of polysiloxane carbonate block copolymers by the melt transesterification process from bisphenol, diaryl carbonate and silanol end-terminated polysiloxanes in the presence of a catalyst is described in U.S. Pat. No. 5,227,449. The siloxane compounds used are polydiphenyl- or polydimethylsiloxane telomers with silanol end groups. It is known, however, that such dimethylsiloxanes having silanol end groups, in contrast to diphenylsiloxane with silanol end groups, have an increasing tendency to self-condensation with decreasing chain length in an acidic or basic medium, such that incorporation into the copolymer as it forms is made more difficult as a result. Cyclic siloxanes formed in this process remain in the polymer and have an exceptionally disruptive effect in applications in the electrical/electronics sector.
U.S. Pat. No. 5,504,177 describes the preparation of a block copolysiloxane carbonate via melt transesterification from a carbonate-terminated silicone with bisphenol and diaryl carbonate. Because of the great incompatibility of the siloxanes with bisphenol and diaryl carbonate, homogeneous incorporation of the siloxanes into the polycarbonate matrix can be achieved only with very great difficulty, if at all, via the melt transesterification process. Furthermore, the preparation of the block cocondensates proceeding from the monomers is very demanding.
Disadvantages of all these processes are the use of organic solvents in at least one step of the synthesis of the silicone-polycarbonate block copolymers, the use of phosgene as a feedstock and/or the inadequate quality of the cocondensate. More particularly, the synthesis of the cocondensates proceeding from the monomers is very demanding, both in the interfacial process and particularly in the melt transesterification process. For example, in the case of the melt process, a small relative underpressure and low temperatures have to be employed, in order to prevent vaporization and hence removal of the monomers. Only in later reaction stages in which oligomers with higher molar mass have formed can lower pressures and higher temperatures be employed. This means that the reaction has to be conducted over several stages and that the reaction times are accordingly long. Furthermore, there is a risk that production process residues such as low-molecular siloxane components remain in the co-condensate.
It is known that branching can have an effect on the rheological properties of polycarbonates. For instance, branched polycarbonates exhibit high structural viscosity. This is used in extrusion processes, e.g. production of water bottles or multi-skin sheets. The preparation of such branched polycarbonates is well known and described in EP 649724. In addition to the manufacturing of branched polycarbonates via the interfacial process with phosgene, the preparation of branched polycarbonates via the melt transesterification process is also known and described in EP 2374829. In these processes, branching is achieved by the use of multifunctional compounds, such as 1,1,1-tris-(4-hydroxyphenyl)ethane. Interestingly, these defective structures also lead to branching, but they have a disadvantageous effect on the rheology of the resultant polycarbonates during processing thereof (EP 2374829).
DE 19710081 describes a process for preparing the cocondensates mentioned in a melt transesterification process proceeding from an oligocarbonate and a specific hydroxyarylsiloxane. The preparation of the oligocarbonate is also described in this application. However, the industrial scale preparation of oligocarbonates for preparation of relatively small-volume specific cocondensates is very costly and inconvenient. Furthermore, the resulting material is unsuitable for the preparation of cocondensates, since the high concentration of OH end groups and other impurities, for example catalyst residue constituents, lead to a poor colour in the end product.
Nowadays, polycarbonates are industrially manufactured from the monomers, i.e. from low molecular weight bisphenols and organic carbonates such as diphenyl carbonate, which is very demanding and requires a costly standard polycarbonate synthesis or copolycarbonate synthesis in a corresponding industrial scale plant
None of the abovementioned applications describes polysiloxane-polycarbonate block cocondensates comprising particular rearrangement structures. Further, siloxane-containing block condensates derived from commercially available polycarbonates and siloxane-components having a molecular weight of more than 3000 g/mol and exhibiting high flowability under shear have not yet been described in the art. These products are advantageous because their preparation requires neither large industrial facilities, such as those for the interfacial polycondensation process, nor toxic feedstocks, such as phosgene.